Input: ads7846 - fix cache line sharing issue

We had a report a while back that the ads7846 driver had some issues
when used with DMA-based SPI controllers (like atmel_spi) on systems
where main memory is not DMA-coherent (most non-x86 boards). Allocate
memory potentially used for DMA separately to avoid cache line issues.
Reported-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/touchscreen/ads7846.c

@@ -69,6 +69,17 @@ struct ts_event {
 	int	ignore;
 };
 
+/*
+ * We allocate this separately to avoid cache line sharing issues when
+ * driver is used with DMA-based SPI controllers (like atmel_spi) on
+ * systems where main memory is not DMA-coherent (most non-x86 boards).
+ */
+struct ads7846_packet {
+	u8			read_x, read_y, read_z1, read_z2, pwrdown;
+	u16			dummy;		/* for the pwrdown read */
+	struct ts_event		tc;
+};
+
 struct ads7846 {
 	struct input_dev	*input;
 	char			phys[32];
@@ -86,9 +97,7 @@ struct ads7846 {
 	u16			x_plate_ohms;
 	u16			pressure_max;
 
-	u8			read_x, read_y, read_z1, read_z2, pwrdown;
-	u16			dummy;		/* for the pwrdown read */
-	struct ts_event		tc;
+	struct ads7846_packet	*packet;
 
 	struct spi_transfer	xfer[18];
 	struct spi_message	msg[5];
@@ -513,16 +522,17 @@ static int get_pendown_state(struct ads7846 *ts)
 static void ads7846_rx(void *ads)
 {
 	struct ads7846		*ts = ads;
+	struct ads7846_packet	*packet = ts->packet;
 	unsigned		Rt;
 	u16			x, y, z1, z2;
 
 	/* ads7846_rx_val() did in-place conversion (including byteswap) from
 	 * on-the-wire format as part of debouncing to get stable readings.
 	 */
-	x = ts->tc.x;
-	y = ts->tc.y;
-	z1 = ts->tc.z1;
-	z2 = ts->tc.z2;
+	x = packet->tc.x;
+	y = packet->tc.y;
+	z1 = packet->tc.z1;
+	z2 = packet->tc.z2;
 
 	/* range filtering */
 	if (x == MAX_12BIT)
@@ -546,10 +556,10 @@ static void ads7846_rx(void *ads)
 	 * the maximum. Don't report it to user space, repeat at least
 	 * once more the measurement
 	 */
-	if (ts->tc.ignore || Rt > ts->pressure_max) {
+	if (packet->tc.ignore || Rt > ts->pressure_max) {
 #ifdef VERBOSE
 		pr_debug("%s: ignored %d pressure %d\n",
-			ts->spi->dev.bus_id, ts->tc.ignore, Rt);
+			ts->spi->dev.bus_id, packet->tc.ignore, Rt);
 #endif
 		hrtimer_start(&ts->timer, ktime_set(0, TS_POLL_PERIOD),
 			      HRTIMER_MODE_REL);
@@ -642,6 +652,7 @@ static int ads7846_no_filter(void *ads, int data_idx, int *val)
 static void ads7846_rx_val(void *ads)
 {
 	struct ads7846 *ts = ads;
+	struct ads7846_packet *packet = ts->packet;
 	struct spi_message *m;
 	struct spi_transfer *t;
 	int val;
@@ -661,7 +672,7 @@ static void ads7846_rx_val(void *ads)
 	case ADS7846_FILTER_REPEAT:
 		break;
 	case ADS7846_FILTER_IGNORE:
-		ts->tc.ignore = 1;
+		packet->tc.ignore = 1;
 		/* Last message will contain ads7846_rx() as the
 		 * completion function.
 		 */
@@ -669,7 +680,7 @@ static void ads7846_rx_val(void *ads)
 		break;
 	case ADS7846_FILTER_OK:
 		*(u16 *)t->rx_buf = val;
-		ts->tc.ignore = 0;
+		packet->tc.ignore = 0;
 		m = &ts->msg[++ts->msg_idx];
 		break;
 	default:
@@ -774,7 +785,6 @@ static void ads7846_disable(struct ads7846 *ts)
 	/* we know the chip's in lowpower mode since we always
 	 * leave it that way after every request
 	 */
-
 }
 
 /* Must be called with ts->lock held */
@@ -850,6 +860,7 @@ static int __devinit setup_pendown(struct spi_device *spi, struct ads7846 *ts)
 static int __devinit ads7846_probe(struct spi_device *spi)
 {
 	struct ads7846			*ts;
+	struct ads7846_packet		*packet;
 	struct input_dev		*input_dev;
 	struct ads7846_platform_data	*pdata = spi->dev.platform_data;
 	struct spi_message		*m;
@@ -885,14 +896,16 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 		return err;
 
 	ts = kzalloc(sizeof(struct ads7846), GFP_KERNEL);
+	packet = kzalloc(sizeof(struct ads7846_packet), GFP_KERNEL);
 	input_dev = input_allocate_device();
-	if (!ts || !input_dev) {
+	if (!ts || !packet || !input_dev) {
 		err = -ENOMEM;
 		goto err_free_mem;
 	}
 
 	dev_set_drvdata(&spi->dev, ts);
 
+	ts->packet = packet;
 	ts->spi = spi;
 	ts->input = input_dev;
 	ts->vref_mv = pdata->vref_mv;
@@ -964,13 +977,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 	spi_message_init(m);
 
 	/* y- still on; turn on only y+ (and ADC) */
-	ts->read_y = READ_Y(vref);
-	x->tx_buf = &ts->read_y;
+	packet->read_y = READ_Y(vref);
+	x->tx_buf = &packet->read_y;
 	x->len = 1;
 	spi_message_add_tail(x, m);
 
 	x++;
-	x->rx_buf = &ts->tc.y;
+	x->rx_buf = &packet->tc.y;
 	x->len = 2;
 	spi_message_add_tail(x, m);
 
@@ -982,12 +995,12 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 		x->delay_usecs = pdata->settle_delay_usecs;
 
 		x++;
-		x->tx_buf = &ts->read_y;
+		x->tx_buf = &packet->read_y;
 		x->len = 1;
 		spi_message_add_tail(x, m);
 
 		x++;
-		x->rx_buf = &ts->tc.y;
+		x->rx_buf = &packet->tc.y;
 		x->len = 2;
 		spi_message_add_tail(x, m);
 	}
@@ -1000,13 +1013,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 
 	/* turn y- off, x+ on, then leave in lowpower */
 	x++;
-	ts->read_x = READ_X(vref);
-	x->tx_buf = &ts->read_x;
+	packet->read_x = READ_X(vref);
+	x->tx_buf = &packet->read_x;
 	x->len = 1;
 	spi_message_add_tail(x, m);
 
 	x++;
-	x->rx_buf = &ts->tc.x;
+	x->rx_buf = &packet->tc.x;
 	x->len = 2;
 	spi_message_add_tail(x, m);
 
@@ -1015,12 +1028,12 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 		x->delay_usecs = pdata->settle_delay_usecs;
 
 		x++;
-		x->tx_buf = &ts->read_x;
+		x->tx_buf = &packet->read_x;
 		x->len = 1;
 		spi_message_add_tail(x, m);
 
 		x++;
-		x->rx_buf = &ts->tc.x;
+		x->rx_buf = &packet->tc.x;
 		x->len = 2;
 		spi_message_add_tail(x, m);
 	}
@@ -1034,13 +1047,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 		spi_message_init(m);
 
 		x++;
-		ts->read_z1 = READ_Z1(vref);
-		x->tx_buf = &ts->read_z1;
+		packet->read_z1 = READ_Z1(vref);
+		x->tx_buf = &packet->read_z1;
 		x->len = 1;
 		spi_message_add_tail(x, m);
 
 		x++;
-		x->rx_buf = &ts->tc.z1;
+		x->rx_buf = &packet->tc.z1;
 		x->len = 2;
 		spi_message_add_tail(x, m);
 
@@ -1049,12 +1062,12 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 			x->delay_usecs = pdata->settle_delay_usecs;
 
 			x++;
-			x->tx_buf = &ts->read_z1;
+			x->tx_buf = &packet->read_z1;
 			x->len = 1;
 			spi_message_add_tail(x, m);
 
 			x++;
-			x->rx_buf = &ts->tc.z1;
+			x->rx_buf = &packet->tc.z1;
 			x->len = 2;
 			spi_message_add_tail(x, m);
 		}
@@ -1066,13 +1079,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 		spi_message_init(m);
 
 		x++;
-		ts->read_z2 = READ_Z2(vref);
-		x->tx_buf = &ts->read_z2;
+		packet->read_z2 = READ_Z2(vref);
+		x->tx_buf = &packet->read_z2;
 		x->len = 1;
 		spi_message_add_tail(x, m);
 
 		x++;
-		x->rx_buf = &ts->tc.z2;
+		x->rx_buf = &packet->tc.z2;
 		x->len = 2;
 		spi_message_add_tail(x, m);
 
@@ -1081,12 +1094,12 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 			x->delay_usecs = pdata->settle_delay_usecs;
 
 			x++;
-			x->tx_buf = &ts->read_z2;
+			x->tx_buf = &packet->read_z2;
 			x->len = 1;
 			spi_message_add_tail(x, m);
 
 			x++;
-			x->rx_buf = &ts->tc.z2;
+			x->rx_buf = &packet->tc.z2;
 			x->len = 2;
 			spi_message_add_tail(x, m);
 		}
@@ -1100,13 +1113,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 	spi_message_init(m);
 
 	x++;
-	ts->pwrdown = PWRDOWN;
-	x->tx_buf = &ts->pwrdown;
+	packet->pwrdown = PWRDOWN;
+	x->tx_buf = &packet->pwrdown;
 	x->len = 1;
 	spi_message_add_tail(x, m);
 
 	x++;
-	x->rx_buf = &ts->dummy;
+	x->rx_buf = &packet->dummy;
 	x->len = 2;
 	CS_CHANGE(*x);
 	spi_message_add_tail(x, m);
@@ -1159,6 +1172,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 		ts->filter_cleanup(ts->filter_data);
  err_free_mem:
 	input_free_device(input_dev);
+	kfree(packet);
 	kfree(ts);
 	return err;
 }
@@ -1184,6 +1198,7 @@ static int __devexit ads7846_remove(struct spi_device *spi)
 	if (ts->filter_cleanup)
 		ts->filter_cleanup(ts->filter_data);
 
+	kfree(ts->packet);
 	kfree(ts);
 
 	dev_dbg(&spi->dev, "unregistered touchscreen\n");